1995 60 HP Merc. not running smoothly at 5 to 6 thousand rpm, "surges".

[60hpmercguy]

Hello all, I have a 1995 60 HP Mercury that runs great at any speed other than between 5 to 6 thousand rpm. This problem just started recently with nothing being changed about the engine or fuel etc. I did change the fuel/water separator to try and fix, but no change. The engine runs as if it you are quickly accelerating and decelerating with the throttle lever and the tach. shows the rpm changing too, but you can accelerate to WOT and it runs great with good response. Adversely, you can drop to less than 5k and the engine runs smoothly. Of course, these are not exact rpm readings but close. At WOT, the tach. indicates close to 7 K rpm. Does this sound like a fuel or ignition problem? What remedies does anyone suggest? Any ideas at all? Thanks

 

[MH Hawker]

Check the timing advance, it may be sticking and not going to the full range of movement.

 

[60hpmercguy]

Hey James or Deb. Thanks for the response. I will check on the timing advance. I do have to learn some more about it before I can do it though. I know the timing advance works with the carburaters as they are accelerated and such. Know of any videos on utube or elsewhere that might be of help? (just love pictures, lol) BTW, I checked out your site on the fishing pontoon you're building, looks like you're doing a good job there. Ought to work well, good luck with it.

 

[enginepower]

Sounds more like a prop problem. It's either slipping or bent blade. You shouldn't be hitting 7k.

 

[Texasmark]

How about some history on the 7k number. What did it used to read before your problem? If it ran in the more normal range of 5000 or so then I'll agree with enginepower. If it has run like that always then you may have the wrong pitched prop or your tach is on the incorrect setting. 12 pole alternators need to be sitting on 6P on the dial on the rear of the tach. If all that is in order then you could have some crud in/around your high speed jet on one of your carbs. The high speed jet is located in the bottom of the carb. bowl. It's a brass screw with a little hole in the end. A good cleaning and good blowing out with 100 or so psig of compressed air is in order.

Mark

 

[60hpmercguy]

Thanks for all the input. The engine has run at about 7K at WOT for years with no trouble. Of course, this may not be completely accurate and if so, the other rpm readings when the engine is not running smoothly are incorrect also. I also checked a while back into changing props (looking to get a spare prop) and verified with the manufacturer as to what the boat actually came with from the factory and they did verify that the prop on the motor now is correct. ie, that's what it came with from the factory. It's and 8 pitch prop. I'm not too concerned with the tach readings, just trying to resolve the erratic running. The boat is a 1995 year model 21 foot tracker pontoon boat. The engine is a Mercury Tracker Pro Series 60.

 

[60hpmercguy]

Little more info on the propeller. The numbers on the prop are 48 42738 A10 8P. Does that indicate an 8 pitch prop?

 

[60hpmercguy]

Little more info on the propeller. The numbers on the prop are 48 42738 A10 8P. Does that indicate an 8 pitch prop? Would love to get a little more speed from the old boat at some point too. So what prop do you recommend to gain a little more speed? I know it's not a speed demon but a little more would be nice. Thanks

 

[Texasmark]

Yes on the 8" pitch.